Magical practices lures many curious visitors, some good, some not so good. Even when you are doing something for good with positive energies, these forces can stay there feasting on the energies (they like it). If they see they can have fun with you, they will.
This is not saying there will always be a bad spirit when magic is performed. Sometimes we have bad dreams for things we have unbalanced; or bad vibes picked up from some people.
Are you properly cleansing? Or do you live with someone that could be giving you bad energies?
Remember having bad dreams, does not necessarily have to be attributed to your magical actions. They could be so many other things.